38 research outputs found
Fractal Reconnection in Solar and Stellar Environments
Recent space based observations of the Sun revealed that magnetic
reconnection is ubiquitous in the solar atmosphere, ranging from small scale
reconnection (observed as nanoflares) to large scale one (observed as long
duration flares or giant arcades). Often the magnetic reconnection events are
associated with mass ejections or jets, which seem to be closely related to
multiple plasmoid ejections from fractal current sheet. The bursty radio and
hard X-ray emissions from flares also suggest the fractal reconnection and
associated particle acceleration. We shall discuss recent observations and
theories related to the plasmoid-induced-reconnection and the fractal
reconnection in solar flares, and their implication to reconnection physics and
particle acceleration. Recent findings of many superflares on solar type stars
that has extended the applicability of the fractal reconnection model of solar
flares to much a wider parameter space suitable for stellar flares are also
discussed.Comment: Invited chapter to appear in "Magnetic Reconnection: Concepts and
Applications", Springer-Verlag, W. D. Gonzalez and E. N. Parker, eds. (2016),
33 pages, 18 figure
An Overview of the 2014 ALMA Long Baseline Campaign
A major goal of the Atacama Large Millimeter/submillimeter Array (ALMA) is to
make accurate images with resolutions of tens of milliarcseconds, which at
submillimeter (submm) wavelengths requires baselines up to ~15 km. To develop
and test this capability, a Long Baseline Campaign (LBC) was carried out from
September to late November 2014, culminating in end-to-end observations,
calibrations, and imaging of selected Science Verification (SV) targets. This
paper presents an overview of the campaign and its main results, including an
investigation of the short-term coherence properties and systematic phase
errors over the long baselines at the ALMA site, a summary of the SV targets
and observations, and recommendations for science observing strategies at long
baselines. Deep ALMA images of the quasar 3C138 at 97 and 241 GHz are also
compared to VLA 43 GHz results, demonstrating an agreement at a level of a few
percent. As a result of the extensive program of LBC testing, the highly
successful SV imaging at long baselines achieved angular resolutions as fine as
19 mas at ~350 GHz. Observing with ALMA on baselines of up to 15 km is now
possible, and opens up new parameter space for submm astronomy.Comment: 11 pages, 7 figures, 2 tables; accepted for publication in the
Astrophysical Journal Letters; this version with small changes to
affiliation
The 2014 ALMA Long Baseline Campaign: An Overview
A major goal of the Atacama Large Millimeter/submillimeter Array (ALMA) is to make accurate images with resolutions of tens of milliarcseconds, which at submillimeter (submm) wavelengths requires baselines up to ~15 km. To develop and test this capability, a Long Baseline Campaign (LBC) was carried out from September to late November 2014, culminating in end-to-end observations, calibrations, and imaging of selected Science Verification (SV) targets. This paper presents an overview of the campaign and its main results, including an investigation of the short-term coherence properties and systematic phase errors over the long baselines at the ALMA site, a summary of the SV targets and observations, and recommendations for science observing strategies at long baselines. Deep ALMA images of the quasar 3C138 at 97 and 241 GHz are also compared to VLA 43 GHz results, demonstrating an agreement at a level of a few percent. As a result of the extensive program of LBC testing, the highly successful SV imaging at long baselines achieved angular resolutions as fine as 19 mas at ~350 GHz. Observing with ALMA on baselines of up to 15 km is now possible, and opens up new parameter space for submm astronomy
Filament destabilization and CME release during a long duration flare
Context. During complex and long duration solar flares, several filament destabilizations or eruptions can occur that are often related to coronal mass ejections (CMEs).
Aims. We describe the study of an X3.8 long duration event (LDE) that occurred in NOAA 10720 on 17 January 2005 and was characterized by three filament destabilizations and two CMEs.
Methods. Using multi-wavelength data provided by both ground-based instruments and satellites, in addition to MDI magnetograms, we investigated the morphological and magnetic evolution of the active region before and during the LDE.
Results. Our analysis of Hα and 1600 Å images showed that initially a two-ribbon structure developed in the central part of the active region, where a filament was previously observed. At a later time, two bright ribbons (in the most eastern side) and a strong brightness increase (at the western outskirt of the active region) were simultaneously observed. In a subsequent time interval, a new pair of ribbons was observed in the western side of the active region. Moreover, a linear force-free field extrapolation helped identify a null point in the central part of the active region.
Conclusions. The initial filament destabilization that occurred in the central part of NOAA 10720 was probably due to magnetic flux emergence and photospheric shearing motions, which caused a slow tether-cutting process beneath the filament. The rearrangement of the magnetic field configuration, occurring in the same area as the location of the null point, changed the magnetic field connectivity in the active region, triggering two filament eruptions in the eastern and western part of the active region and two halo CMEs, in a kind of domino effect
Komplexni hodnoceni uzitku vystavby dopravni infrastruktury.
Available from STL Prague, CZ / NTK - National Technical LibrarySIGLECZCzech Republi
The X17.2 flare occurred in NOAA 10486: an example of filament destabilization caused by a domino effect
Context. It is now possible to distinguish between two main models describing the mechanisms responsible for eruptive flares : the standard model, which assumes that most of the energy is released, by magnetic reconnection, in the region hosting the core of a sheared magnetic field, and the breakout model, which assumes reconnection occurs at first in a magnetic arcade overlaying the eruptive features.
Aims. We analyze the phenomena observed in NOAA 10486 before and during an X17.2 flare that occurred on 2003 October 28, to study the relationship between the pre-flare and flare phases and determine which model is the most suitable for interpreting this event.
Methods. We performed an analysis of multiwavelength data set available for the event using radio data (0.8–4.5 GHz), images in the visible range (WL and Hα), EUV images (1600 and 195 Å), and X-ray data, as well as MDI longitudinal magnetograms. We determined the temporal sequence of events occurring before and during the X17.2 flare and the magnetic field configuration in the linear force-free field approximation.
Results. The active region was characterized by a multiple arcade configuration and the X17.2 flare was preceded, by ~2Â h, by the partial eruption of one filament. This eruption caused reconnection at null points located in the low atmosphere and a decrease in magnetic tension in the coronal field lines overlaying other filaments present in the active region. As a consequence, these filaments were destabilized and the X17.2 flare occurred.
Conclusions. The phenomena observed in NOAAÂ 10486 before and during the X17.2 flare cannot be explained by a simple scenario such as the standard or breakout model, but instead in terms of a so-called domino effect, involving a sequence of destabilizing processes that triggered the flare